Wound magnetic core and method of forming same

ABSTRACT

A WOUND CORE HAVING A PLURALITY OF TURNS OF MAGNETIC STRIP MATERIAL WITH A PREDETERMINED AMOUNT OF LOOSENESS BETWEEN THE SUPERPOSED TURNS, AND AT LEAST ONE SPACE BETWEEN ADJACENT SUPERPOSED TURNS HAVING A DEGREE OF LOOSENESS PREDETERMINATELY GREATER THAN THAT BETWEEN THE OTHER TURNS. THE SUPERPOSED TURNS OF SAID WOUND CORE ARE ROTATED IN ONE DIRECTION TO OBTAIN THE PREDETERMINED LOOSENESS AND THEN ROTATED IN THE OTHER DIRECTION TO REDISTRIBUTE A PORTION OF SAID LOOSENESS INTO A DESIRED SECTION OF THE CORE.

Sept. 1971 J. a. MKEE 3,603,343

WOUND MAGNETIC CORE AND METHOD OF FORIING SAIE Filed July 7,1969 2Sheets-Sheet 1 mvsmon JOHN B. McKEE J. B. M KEE Sept. 28, 1971 WOUNDMAGNETIC CORE AND METHOD OF FORMING SAME 2 Sheets-Sheet 2 Filed July '7,1969 22 &

FIG. 8-

FIG- 10 lllllll FIG. 13

INVENTOR JOHN B. McKEE FIG. 12

United States Patent ice 3,608,348 WOUND MAGNETIC CORE AND METHOD OFFORMING SAME John B. McKee, Glendale, Mo., assignor to Wagner ElectricCorporation, Newark, N.Y. Filed July 7, 1969, Ser. No. 839,300 Int. Cl.B21c 47/02 U.S. Cl. 72-146 12 Claims ABSTRACT OF THE DISCLOSURE A woundcore having a plurality of turns of magnetic strip material with apredetermined amount of looseness between the superposed turns, and atleast one space between adjacent superposed turns having a degree oflooseness predeterminately greater than that between the other turns.The superposed turns of said wound core are rotated in one direction toobtain the predetermined looseness and then rotated in the otherdirection to redistribute a portion of said looseness into a desiredsection of the core.

This invention relates to wound magnetic cores for induction apparatusand to a method of making such magnetic cores of the wound type.

In the past, wound cores were formed by winding a plurality ofsuperposed turns of continuous magnetic strip material onto a rotatablemandrel into an annular or ringshaped core which was subsequentlyreshaped into the desired substantially rectangular form and annealednot only to relieve the stresses therein but also to impart a permanentset thereto in said desired reshaped form. After annealing, the reshapedcore Was unwound and simultaneously cut into sections comprised of adesired number of turns, and such out turn sections were then rewound orrepositioned in their predetermined order into an assembled finishedcore about a conductive coil structure.

During the initial winding of the strip material, a certain degree oflooseness or slack between the superposed turns thereof was provided bythe well-known method of inserting sacrificing material, such as nylonthread, paper, or other shims or spacers, between the superposed turns,or by predeterminately crimping the strip material itself. Suchlooseness in the core was, of course, provided in an attempt tocompensate for excessive stress imparted to the out turn sections uponthe subsequent reassembly thereof about the coil structure so that thefinished core of the reassembled cut turn sections on the coil structureapproximated the size, shape and position of the annealed core prior tothe unwinding and cutting of said turn sections. One of thedisadvantageous or undesirable features of such past cores and methodsof assembly thereof was that it was virtually impossible to obtain thecorrect or desired amount of slack in each core which is necessary forproper reassembly of the cut turn sections thereof because of the greatvariance in the thickness of the strip material, the variance in thetension used to initially wind the strip material, and the variance inthe slidability between the turns of the strip material. Too much slackbetween the adjacent turns of said past cores was undesirable since itincreased the means length of each turn and made the core larger thannecessary or desired. Another disadvantageous or undesirable feature ofthe previous cores and the previous methods of imparting slack orlooseness to the core was that a substantially uniform space factor wasusually provided between the superposed turns. For instance, thoseskilled in the art have found from experience that such a uniform spacefactor is satisfactory only within a stack height range approximatingone-half inch to three-fourths of an inch of superposed turns. Withinthis range, the adjacent ends of the successive cut 3,668,348 PatentedSept. 28, 1971 turn sections would abut each other or so closelyapproximate each other as to form a butt joint which afforded the coredesirable magnetic characteristics and a low destructability factor. Thereason for such approximate stack height range is, of course, that theout turn sections within such range are not overstressed when rewoundinto finished position about the coil structure; however, as the stackheight increased, the out turn sections were stressed in excess of adesired amount as they are rewound into finished position about saidcoil structure. Therefore, due to the overstressing in the reassembly ofthe cut turn sections, another disadvantageous or undesirable featurewas that said cut turn sections would not return to their annealed shaperesulting in a gap between the adjacent ends of the out turn sections,and as the stack height increased in excess of the range, said gapsbecame progressively larger which, of course, adversely affected themagnetic characteristics and destructibility factor of the core. Stillanother disadvantageous or undesirable feature was that as the stackheight increased in excess of the range, the end or yoke portion of thecore in which the gaps are formed built up; therefore, the stack heightof the core in said yoke became appreciably greater than that in anadjacent leg portion, and this was due to the inability of the out turnsections to return to their annealed shape upon the aforementionedoverstressing thereof during as-.

bility thereof was adversely affected. Furthermore, still anotherdisadvantageous or undesirable feature was that a spongy core would alsoslump appreciably when support mg its own weight to further depart fromthe desired substantially rectangular configuration.

The principal object of the present invention is to provide a wound coreand a method of making such wound core which overcomes theaforementioned disadvantageous and undesirable features of the pastwound cores and the past methods of forming wound cores, as well asother disadvantageous and undesirable features thereof, and this andother advantageous and desirable features of the present invention willbecome apparent in the specification which follows.

Briefly, the present invention includes a wound core having thelooseness between the adjacent superposed turns of magnetic stripmaterial predetermined in progressively increasing amounts in adirection from the inner perimeter toward the outer perimeter of saidcore. Another aspect of the invention provides at least one space gapselectively provided at a desired position in the stack height of saidturns having a degree of looseness greater than that between the otherof said turns. The invention also includes a method of winding aplurality of superposed turns of magnetic strip material to form anannular core substantially without slack between said turns, rotatingsaid turns to obtain predetermined slack distribution in progressivelyincreasing amounts in a direction from the inner perimeter toward theouter perimeter of said core throughout at least a portion of the core.

In the drawings which form a part of the specification and wherein likenumerals refer to like parts wherever they occur:

FIG. 1 is a diagrammatic view illustrating the winding of magnetic stripmaterial into a wound core;

FIG. 2 is an enlarged elevational view of the wound core of FIG. 1illustrating the displacement of the outer turn to predetermine the coreoutside diameter and the amount of slack to be inserted into said core;

FIG. 3 is an elevational view showing the core of FIG. 2 with the turnsthereof in their adjusted unwound positions upon rotation of the coreturns in a direction opposite the winding direction;

FIG. 4 is a greatly enlarged fragmentary view taken from FIG. 3illustrating the predetermined space factor or slack distributionbetween the adjacent superposed core turns in their adjusted unwoundpositions;

FIG. 5 is a partial sectional view of the wound core showing a tool forrewinding the core turns in the winding direction;

FIG. 6 is a greatly enlarged fragmentary view illustrating thepredetermined space factor or slack distribution between the adjacentsuperposed core turns and also the space gaps provided in said core uponthe rewinding of said core turns in the winding direction onto the tool;

FIG. 7 is an elevational view of the core with the turns thereof intheir rewound positions upon the rewinding of said turns onto the tool;

FIG. 8 is an elevational view of another wound core embodying thepresent invention in which the outer turn is wound to a predetermineddiameter and the inner turn thereof is slightly greater than apreselected inner diameter of said core;

FIG. 9 is an elevational view showing a finished wound core placed in apress for the shaping thereof;

FIG. 10 is an elevational view illustrating the shaping of the finishedwound core into the desired rectangular shape by the press;

FIG. 11 is a greatly enlarged fragmentary view taken from FIG. 10illustrating the redistribution of the space gaps into the corners ofthe shaped core;

FIG. 12 is an elevational view illustrating the annealed and out turnsections which are unwound from the shaped core; and

FIG. 13 is a partial sectional view of the conductive winding structurelinked by a magnetic core made in accordance with the present invention.

Referring now to the drawings and in particular to FIG. 1, magneticstrip material 1, such as grain oriented silicon steel strip, is drawnfrom a supply spool 2 thereof in a winding direction shown by thedirectional arrow onto a driven, rotatable, annular mandrel or arbor 3forming a wound core 4 of superposed, spirally wound turns 5, and adesired turn tension is maintained during winding by passing said stripmaterial through an adjustable tensioning device, such as opposedrollers 6 in a manner well known in the art. The leading end of thestrip material is bent at 5a as said strip material is lead onto thearbor 3 from the supply spool 2, and, of course, the tensioning of thestrip material 1 during winding produces the desired effect ofsubstantially eliminating slack or space between the turns 5 of theinitially wound core 4. In one aspect of the invention, the diameter ofthe arbor 3 substantially conforms to the desired inside or windowdiameter or perimeter for the wound core 4, and said core is wound to apredetermined stack height of turns 5 afiording a desired orpredetermined cross-sectional turn area and also the desired pounds ofstrip material 1 for the particular core size. As mentioned above, theinside diameter of the wound core 4 is maintained to the desiredpredetermined diameter, and upon winding the predetermined stack heightof turns 5, the outside diameter or perimeter of said core ispredeterminately undersized. When the pre determined stack height ofturns 5 is so wound on the arbor 3 to form the desired core 4, the stripmaterial is severed by cutters 7 in a manner well known in the art, andsaid core is removed from said arbor.

After the initial winding of the core 4, the free end 8 of the outsideturn 9 of said core is then displaced or set-ofl. a predetermineddistance or amount S relative to the next adjacent turn 10, as shown inFIG. 2, and such displacement represents the predetermined amount oflooseness or slack to be subsequently inserted or placed in the core andis substantially equal to the difference between the undersized outsideperimeter or circumference of said core as wound and the predeterminedoutside perimeter or circumference desired in the finished core. Inother words, the outside diameter or perimeter of the core 4 asinitially wound on the arbor 3 was predeterminately undersized, asmentioned hereinbefore, so that the displacement S of the free end 8 ofthe outer turn 9 relative to the next adjacent turn 10 not onlypredetermines the amount of slack to be inserted into said core but alsoadjusts or increases the outside diameter to the predetermined dimensiondesired for the finished core. In order to maintain the outside turnfree end 8 in its displaced position, the outside turn 9 is restrainedor is connected by suitable means, such as the tape 11, to the adjacentturn 10; however, albeit not shown, such connection could, if desired,be accomplished by other means, such as spot welding or clamping, or theinitially wound core could be placed in a retaining ring having thedesired outside diameter of the finished core. It should be noted thatthe bent or free end 5a of the inside turn 13 of the coil isunrestrained against movement relative to its next adjacent turn 14.

With the outside and next adjacent turns 9, 10 so connected, the-core 4is rotated in a direction opposite to the winding direction indicated bythe arrow to distribute the slack effected by the displacement S of theouter turn 8 throughout said core, as shown in FIGS. 3 and 4. In otherwords, a rotative force is applied onto the outside turn 9 to initiatethe rotation of the interconnected outside and next adjacent turns 9, 10of the core 4 in the direction opposite to the arrow and continuedrotation effects a partial and successive unwinding and realignment ofthe superposed turns 5 radially outwardly toward new or adjustedpositions commensurate with the adjusted outside diameter of the core 4which was established upon the predetermined displacement of the outsideturn free end 8, and at the same time, the slack occasioned upon thepredetermined displacement of said outside turn free end is distributedin a substantially uniform manner or substantially equal amounts betweeneach of the adjacent superposed turns 5 in their adjusted positions. Forinstance, as the core 4 is being rotated, the outermost of the turns 5move radially outwardly in succession; therefore, as core rotationprogresses, the successive radially outward movement of said turnseffects a greater mass for rotation and such a greater mass effects agreater inter-turn friction or drag opposing rotation. The increasingdrag opposing the mass of said turns 5 being rotated effects aprogressively varying tensioning force which controls the substantiallyuniform manner in which the slack is inserted into the core. Forinstance, during the initial rotation of the core 4, there is verylittle drag since the mass of the turns 5 being rotated, i.e., thoseturns which have been unwound radially outwardly to their adjustedpositions, is quite small compared to the rest of the mass of the coreturns which are substantially stationary; therefore, the outermost ofsaid turns are unwound rather tightly in their adjusted positions withrespect to each other, but as the mass of the radially outer turns 5being rotated increases upon further rotation, the drag thereof is alsoproportionally increased to eifect successively greater distancesbetween adjacent turns in a radial direction from the outer toward theinner perimeter of the core 4. In other words, the increasing dragoccasioned upon the successive unwinding movement of the turns 5radially outwardly toward their adjusted positions effects a spacefactor or radial distance between each adjacent turn which increasesincrementally in a radial direction from the outside toward the insideperimeter of the core, as shown greatly exaggerated in FIG. 4;therefore, due to the incrementally increasing space factor, thepredetermined amount of slack is inserted or distributed between eachadjacent turn in substantially equal or uniform amounts throughout thestack height 5. It should be noted that while the outside diameter ofthe core 4 was adjusted to the desired dimension, the distribution ofthe predetermined amount of slack into said core does not appreciablyincrease or adjust the predetermined inside perimeter or diameter aswound on the arbor 3.

A winding tool 15, FIG. 5, is provided with a round disc or base portion16 having a circumference and diameter substantially equal to thedesired predetermined inside circumference and diameter of the core 4.With the predetermined amount of slack uniformly distributed throughoutthe core 4 and turns 5 thereof in their adjusted positions, aspreviously described, the disc portion 16 of the tool is inserted intothe inside perimeter or window portion of the core 4 into interfering ordriving engagement with the inner turn 13 of said core. As shown in FIG.5, the tool 15 may be provided with a slot 16a in the periphery of thetool disc 16, and the free end 5a of the inside turn 13 is inserted intorestraining or driving engagement with said slot to drivingly engagesaid tool with said inside turn; however, other means, such as anexpanding tool or a power-driven tool or the like, are contemplated toeffect such driving engagement.

Rotation of the tool 15 in the winding direction with the free end 5a ofthe inner turn 13 restrained in the tool slot 16a applies a rerotativeforce on said inside turn to effect a partial and successive rewindingand alignment of the turns 5 from their adjusted positions radiallyinwardly toward new or rewound positions about the disc portion 16 ofsaid tool which defines the desired or predetermined inside perimeter ofthe core 4. For instance, as the tool 15 is being rotated, the innermostof the turns 5 move radially inwardly in succession toward the innerturn 13 in its rewound position, and as such rotation progresses, thesuccessive radially inward movement ofsaid turns effects a greater massfor rotation and such increasing mass for rotation effects an increasinginter-turn friction or drag; therefore, due to the proportionedrelationship between the increasing mass and drag, a progressivelyvarying or increasing tensioning force is established which controls thespace factor and distribution of the slack between the adjacent turns intheir rewound positions. During the initial rotation of the tool 15,there is very little drag since the mass of the turns 5 being rotated,i.e., those turns which have been rewound radially inwardly to theirrewound positions, is quite small compared to the rest of the mass ofthe core turns which are substantially stationary; therefore, theinnermost of said turns are rewound on said tool rather tightly in theirrewound positions with respect to each other, but as the mass of therewound turns increases, the drag thereof is also proportionallyincreased to effect successively and incrementally greater distancesbetween each of said adjacent rewound turns in a radial direction fromthe inner perimeter toward the outer perimeter of the core 4. In otherwords, the increasing drag occasioned upon the successive rewindingmovement of the turns 5 radially inwardly toward their rewound positionsefiects a space factor or radial distance between each adjacent rewoundturn which increases incrementally in a radial direction from the insideperimeter toward the outside perimeter of the core, as shown in FIG. 6;therefore, since the space factor between each adjacent rewound turn isincreased incrementally in the radially outward direction, it isapparent that the predetermined amount of slack is redistributed betweeneach adjacent rewound turn in an increasing manner or in progressivelyincreasing amounts also in the direction from the inner perimeter towardthe outer perimeter of the core 4.

In view of the foregoing, the amount of slack distributed between theadjacent rewound turns and the space factor therebetween is, of course,less than that between the other turns 5 of the core 4 which are stillin their adjusted positions; therefore, slack take-up is occasioned uponthe successive radially inward movement of the turns 5 from theiradjusted positions to their rewound positions creating a slack or spacegap, indicated generally at 17 in FIG. 7, which can be selectivelypositioned and maintained at any diameter of the stack height of theturns 5 as desired. During the successive rewinding of the turns 5 intotheir rewound positions on the tool 15, the slack gap 17 moves radiallyoutwardly, and when said slack gap approaches a desired diameter orpreselected point in the stack height of the turns 5, the operator canretain or maintain said slack gap at said preselected point or diameterof the stack height by temporarily inserting a clamp or spacer, or othersuch restraining means, into said slack gap or by holding or pressingthe side edges of the adjacent turns on the radially inner and outersides of said slack gap with his fingers or other restraining object. Inthis manner, the slack gap 17 is positioned at the preselected stackheight, and thereafter continued rotation of the tool 15 will againinitiate the successive rewinding of the turns 5 from their adjustedpositions toward their rewound positions adjacent the slack gap 17 toredistribute the remaining slack in the core 4 in the progressivelyincreasing manner, as described above. Although only one slack gap 17 isdescribed, the operator can split up or distribute the slack in theslack gap 17 into other smaller slack gaps, such as that shown at 17a,at several preselected points or diameters in the stack height of theturns 5 in the same manner as previously described wherein said spacegaps 17, 17a divide the stack height of said turn into turn groupsindicated generally at 18, 19 and 20. The space gaps 17, 17a areinserted into the core 4 at various preselected diameters thereof toprovide re-indexing or new reference points or diameters which effectand insure a desirable and tight-fitting core upon the assembly thereofwith a conductive winding structure, as discussed hereinafter.

Referring now to FIG. 8 in another aspect of the invention, another core104 is wound in substantially the same manner and has substantially thesame component parts as the previously described core 4 with thefollowing exceptions. The arbor 3 of FIG. 1 on which the core 104 iswound is provided with a diameter or circumference which is slightlygreater than the preselected inside diameter or perimeter of the core104; therefore, the inside diameter or perimeter of said core asoriginally found is slightly oversized and the outside diameter orperimeter thereof is wound to the predetermined or desired perimeter ofthe finished core. In order to maintain the outside turn free end 8 inits wound or predetermined position, the outside turn 9 is restrained oris connected by suitable means, such as the tape 11, to the nextadjacent turn 10; however, albeit not shown, such connection could, ifdesired, be accomplished by other means, such as spot welding orclamping, or the initially wound core could be placed in a retainingring having the desired or predetermined outside perimeter of thefinished core.

In this aspect of the invention, the operator may elect to rotate theturns 5 of the core 104 from the inside diameter thereof by the use ofthe tool 15 wherein the disc portion 16 thereof is provided with aperimeter which defines the predetermined or desired inside perimeter ofsaid core, as previously mentioned. With the turns 5 of the core 104positioned as originally wound substantially without slack therebetween,the disc portion 16 of the tool 15 is inserted into the inside perimeteror window portion of the core 104 for driving engagement with the innerturn 13 of said core wherein the free end 5a of the inside turn 13 isinserted into restraining or driving engagement with the disc slot 16aof said tool; however, other means, such as an expanding or power-driventool or the like, are contemplated to effect such driving engagement, aspreviously mentioned.

Rotation of the tool 15 in the winding direction with the inner turnfree end a restrained in the tool slot 16a applies a rotative force inthe inside turn 13 to effect a partial and successive rewinding andalignment of the turns 5 from their originally wound positions radiallyinwardly toward new or rewound positions about the disc portion 16 ofsaid tool which defines the predetermined inside perimeter of the core104. For instance, as the tool 15 is being rotated, the innermost of theturns 5 move radially inwardly in succession toward the inner turn 13 inits rewound position, and as such rotation progresses, the successiveradially inward movement of said turns elfects a greater mass forrotation, and such increasing mass for rotation eifects an increasinginter-turn friction or drag; therefore, due to the proportionedrelationships between the increasing mass and drag, a progressivelyvarying or increasing tensioning force is established which controls thespace factor and distribution of the slack between the adjacent turns intheir rewound positions. For instance, during the initial rotation ofthe tool 15, there is very little drag since the mass of the turns 5being rotated, i.e., those turns which have been rewound radiallyinwardly to their rewound positions, is quite small compared to the restof the mass of said core turns which are substantially stationary;therefore, the inner most of said core turns are rewound onto said toolrather tightly in their rewound positions with respect to each other,but as the mass of the rewound turns increases, the drag thereof is alsoproportionally increased to effect successively and incrementallygreater distances between each of said adjacent rewound turns in aradial direction from the inner perimeter toward the outer perimeter ofthe core 104. In other words, the increasing drag occasioned upon thesuccessive rewinding movement of the turns 5 radially inwardly towardtheir rewound positions effects a space factor or radial distancebetween each adjacent rewound turn which increases incrementally in aradial direction from the inside to the outside perimeter of the core104, as shown in FIG. 6; therefore, since the space factor between eachadjacent rewound turn is increased incrementally in the radially outwarddirection, it is apparent that the predetermined amount of slack isdistributed between each adjacent rewound turn in an increasing manneror in progressively increasing amounts also in the direction from theinner perimeter toward the outer perimeter of the core 104.

As previously mentioned, the core 104 was originally wound with asubstantially solid stack height of turns substantially without slacktherebetween; therefore, in view of the insertion of the slack into thecore 104, it is apparent that the radially inward and successivemovement of the turns 5 from their originally wound positions towardtheir rewound positions effects a slack gap therebetween, as indicatedgenerally at 17 in FIGS. 6 and 7, which can be selectively positionedand maintained at any diameter of the stack height of turns, as desired.During the successive rewinding of the turns 5 into their rewoundpositions onto the tool 15, the slack gap 17 moves radially outwardly,and when said slaok gap approaches a desired diameter or preselectedpoint in the stack height of the turns 5, the operator can retain ormaintain said slack gap at said preselected point or diameter of thestack height by temporarily inserting a clamp or spacer, or other suchrestraining means, into said slack gap or by holding or pressing theside edges of the adjacent turns in the radially inner and outer sidesof said slack gap with his fingers or other restraining object. In thismanner, the slack gap 17 is predeterminately positioned at thepreselected stack height, and thereafter continued rotation of the tool15 will again initiate the radially inward and successive rewinding ofthe turns 5 from their originally wound positions toward their rewoundpositions adjacent to the slack gap 17 to distribute the remaining slackthroughout the core 104 in the progressively increasing manner, aspreviously described. Although only one slack gap 17 is described, theoperator can split up or distribute the slack in the slack gap 17 intoother smaller slack gaps, such as shown at 17a, at several preselectedpoints in the stack height of turns 5 in the same manner previouslydescribed wherein said space gaps 17, 17a divide the stack height ofsaid turns into turn groups indicated generally at 18, 19 and 20. Thespace gaps 17, 17a are inserted into or provided in the core 104 at thevarious preselected diameters thereof to provide reindexing or newreference points which effect and insure a desirable and tight-fittingcore upon the assembly thereof with a conductive winding structure, asdiscussed hereinafter.

The finished wound cores 4, 104- as shown in FIG. 7, having thepredetermined amount of slack inserted thereinto and distributedpredeterminately throughout the turns 5 of said core according to any ofthe methods set forth hereinabove is then deformed into the desiredrectangular shape by any one of several Well-known shaping methods. InFIG. 9, for instance, the finished core 4 or 104 is placed in a press 21having opposed stationary sides 22', 23 and opposed movable sides 24,25, and a window block 26 is placed in the window or inner diameter ofsaid core. Opposed forces F F are then applied by suitable means (notshown) on the movable press sides 24, 25 to deform the core 4 into thedesired rectangular shape, as shown in FIG. 10, and as shown in FIG. 11,the slack previously inserted between the adjacent turns 5 and in thespace gaps 17, 17a is repositioned into each of the four corners of theshaped core 4 or 104 to predeterminately create reindexing or referencepoints 27, 27a in the stack height of the turns 5 to facilitate thereassembly of said core onto a conductive winding element, as discussed,hereinafter. The forces F F are then removed from the movable presssides 24, 25, and the shaped core 4 or 104 is removed from the press 21and placed in an annealing furnace (not shown) to relieve stresses insaid shaped core and impart a permanent set thereto, as well known inthe art.

After being removed from the annealing furnace and cooled, the shapedcore 4 or 104 may be linked with a preformed winding structure, inaccordance with one method, by first unwinding the strip material 1 ofsaid shaped core and cutting through said strip material at preselectedspaced intervals to provide a plurality of cut turn sections, as is alsowell known in the art. FIG. 12 shows a plurality of nested out turnsections 31, 32 and 33 each having a preselected length equal toapproximately one 'and a half turns of the shaped core 4. These cut turnsections of strip material may then be linked with an insulatedconductive winding element or structure 34, as shown in FIG. 13. Toassemble the out turn sections 31, 32, 3-3 on the winding structure 34',it is, of course, necessary to spread said cut turn sections as they arebeing rewound about one side of said winding structure, and as the stackheight of said out turn sections is built up about said windingstructure, excessive spreading of said out turn section could effectpermanent distortion thereof which, of course, would adversely affectthe desirable butt jointing of the adjacent ends of said out turnSections and impart a spongeness or stack height build-up in one of theleg or yoke sections of the assembled core 4. However, the slack gaps17, 17:: which define the reindexing points 27, 27a prevent such stackheight build-up in the assembled core 4 by providing a predeterminedamount of slack between the turn groups 18, 19 and 20 wherein the firstturn of each group provides a new reference or indexing point aboutwhich the other turns of said group are assem bled without regard to anystack height build-up which may have been present in the assembly of theturns of the previously assembled group. In other words, the provisionof the reindexing points 27, 27a not only minimizes the possibility oftolerance build-up or stack height build-up in each of the turn groups18, 1Q, 20 upon the assembly of the individual out turn sections 30, 31,32 thereof but also minimizes the cumulative affect of said turn groupswith regard to such stack height build-up, and thereby desirablecloseness with regard to the butt-jointing of the adjacent ends of saidout turn sections is enhanced.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1.--A method of making a wound transformer core from a continuous stripof magnetic material comprising the steps of: spirally winding aplurality of superposed turns of said strip material into an annularstack height of turns substantially without slack therein, said stackheight being wound to a predetermined outer perimeter and having aninner perimeter in excess of that predeterminately desired, moving theinner turn of said stack height'relative to its next adjacent turntoward a displaced position defining the desired predetermined innerperimeter and providing a predetermined amount of slack for distributionin said stackheight, applying a rotative force on the inner turn of saidstack height to effect substantially successive rotative movement of atleast a portion of said turns radially inwardly toward rewound positionsabout said inner turn and simultaneously distribute the slack betweeneach of the adjacent turns in their rewound positions in progressivelyincreas ing amount from the inner perimeter toward the outer perimeterof said stack height.

2. A method according to claim 1, comprising the additional step ofrestraining two selected adjacent turns in said stack height toestablish a slack gap therebetween having an appreciably greater amountof slack than that distributed between the other adjacent turns in theirrewound positions upon the rotation of said turns in response to theapplied rotative force.

3. A method of making a wound transformer core from a continuous stripof magnetic material comprising the steps of: spirally winding aplurality of superposed turns of said strip material into an annularstack height of turns substantially without slack therebetween, saidstack height having a predetermined outer perimeter and an innerperimeter wound predeterminately in excess of that desired, drivinglyengaging a tool having a perimeter defining the desired predeterminedinner perimeter of said stack height with the inner turn thereof, thedifference between the wound inner perimeter of said stack height andthe tool perimeter defining the amount of slack for distribution in saidstack height, driving said tool to apply a rotative force on said innerturn to effect substantially successive rotative movement of said innerturn and at least a portion of the other of said turns radially inwardlytoward rewound positions about said tool perimeter and simultaneouslydistribute the slack between each of the adjacent turns in their rewoundpositions in incremental amounts progressively increasing from the innerperimeter toward the outer perimeter of said stack height.

4. A method according to claim 3, comprising slot means in said too],said slot means being connected with the free end of said inner turnprior to the driving engagement of said tool with said inner turn.

5. A method according to claim 3, comprising the additional step oflimiting the movement of a selected one of said turns relative to thenext adjacent turn thereto in its rewound position to establish a slackgap between said selected one turn and said next adjacent turn theretoin its rewound position separating the turns in their rewound positionfrom the other turns in said stack height, said slack gap defining anappreciably greater amount of slack than that distributed between anyother two adjacent turns in their rewound positions.

6. A method according to claim 3, comprising the step of connecting theouter turn of said stack height with its next adjacent turn againstdisplacement to main- 10 tain the predetermined outer perimeter of saidstack height.

7. A method of making a wound transformer core from a continuous stripof magnetic material comprising the steps of: connecting one end of saidstrip material with a rotatable arbor having a perimeter predeterminately in excess of the desired inner perimeter of said core, rotating saidarbor to spirally wind thereon a plurality of superposed turns of saidstrip material into a stack height of said turns having a predeterminedouter perimeter, severing the other end of said strip material from thesupply thereof when said stack height of turns is wound to itspredetermined outer perimeter, removing said stack height of turns fromsaid arbor and connecting said other end of the outer turn of said stackheight to its next adjacent turn against displacement to maintain thepredetermined outer perimeter of said stack height, engaging a toolhaving a perimeter defining the desired inner perimeter of said stackheight with said one end of the: inner turn of said stack height, thedifference between the perimeter of the inner turn of said stack heightwound on said arbor and the perimeter of said tool predeterminatelydefining the entire amount of slack for distribution between the turnsof said stack height, driving said tool to apply a rotative force onsaid one end of said inner turn effecting substantially successiverotative movement of said inner turn and at least a portion of the otherof said turns radially inwardly toward rewound positions about theperimeter of said tool and simultaneously distributing a portion of saidslack between each of the adjacent turns in their rewound positions inincremental amounts progressively increasing from the inner perimetertoward the outer perimeter of said core.

8. A method according to claim 1, comprising shaping the core to apredetermined shape having yoke and leg members, and annealing said coreto relieve stresses therein.

9. A method according to claim 1, comprising the step of restraining therewinding movement of at least one turn relative to its next adjacentturn in said stack height to establish a slack gap therebetween having agreater amount of distributed slack than that distributed between any ofthe other adjacent turns in their rewound positions during the rotationof said turns to their rewound positions, shaping the core to apredetermined shape having opposed yoke and leg members, and annealingsaid core in its predetermined shape to relieve stresses therein.

10. A method of making a wound transformer core from a continuous stripof magnetic material comprising the steps of: spirally winding aplurality of superposed turns of said strip material into an annularstack height of turns substantially without slack therein, one of theinner and outer perimeters of said stack being predeterminated, movingone of the inner and outer turns of said stack relative to its nextadjacent turn toward a displaced position to predeterminately define theother of the inner and outer perimeters and provide a predeterminedamount of slack for distribution in said stack height, and rotating atleast a portion of said turns of said stack toward rewound positionsabout said inner turn to simultaneously distribute the slack betweeneach adjacent turn in their rewound position in progressively increasingamounts from the inner perimeter toward the outer perimeter of saidstack.

11. A method according to claim 10, comprising the step of restrainingthe movement of at least one turn relative to its next adjacent turn toestablish a slack gap therebetween having a greater amount of slack thanthat distributed between the other adjacent turns in their rewoundpositions during the rotation of said turns toward their rewoundpositions.

12. A method according to claim 11, comprising shaping the core to apredetermined shape having yoke and 2 leg members, and annealing saidcore to relieve stresses 3,223,955 12/1965 Olsen et a1. 29--605 therein.3,406,600 10/1968 Minick 29-426 References Cited UNITED STATES PATENTS 5RICHARD J. HERBST, Pnmary Examlner 2,282,854 5/ 1942 Driftmeyer 2960SUS. Cl. X.R. 3,200,476 8/ 1965 Olsen et al. 29605 29605

